The purpose of the present invention is to provide: a pharmaceutical composition that comprises the pyridylaminoacetic acid compound of the present invention, said pyridylaminoacetic acid compound being stable within the pharmaceutical composition； and a method for improving the stability of the pydridylaminoacetic acid compound within the pharmaceutical composition. The pharmaceutical composition comprises: (6{[4-(pyrazol—1—yl) benzyl] (pyridine—3—ylsulfonyl) aminomethy11pyridine-2-ylamino) isopropyl acetate or a salt thereof； arid polyoxyethylene castor oil. The polyoxyethylene castor oil preferably comprises a polyoxyethylene castor oil selected from the group consisting of polyoxyl 5 castor oil, polyoxyl 9 castor oil, polyoxyl 15 castor oil, polyoxyl 35 castor oil, and polyoxyl 40 castor oil. (No Suitable Figure)
